1. Field of the Invention
This invention pertains to medical engineering, but more particularly to ophthalmology and provides an apparatus adapted to fragment and aspirate ocular tissues relying on the use of ultrasound. This invention will be found most useful in the operative procedures involving the removal of cataract, as well as the vitreous, blood clots, fibrin membranes, and exudates.
2. Description of the Prior Art
At the present time a highly promising technique of cataract extraction consists in fragmenting the opacified lens directly in situ combined with the simultaneous suction of the fragmented mass. This technique is far less traumatic compared to the conventional methods of cataract removal, for example, cryophakia, since it requires an operative incision of but a small size to enable the introduction of a needle or an instrument tip into the eye. A similar situation is seen in respect of excision of the pathologically affected vitreous, as well as in pathological changes involving other tissues (fibrin membranes, blood pools, exudates).
An embodiment of the method relies on the use of mechanical devices, vitreotomes, for example, such as that described in U.S. Pat. No. 3,882,872. The instrument referred to consists of a mechanical drive, aspiration unit, and a working tip shaped as two coaxially arranged tubes interacting by their cutting edges. The tissue to be removed is sucked into the passage between the tubes and is then subjected to the shearing type cutting action while the inner tube moves.
However, such mechanical devices require continuously razor-sharp cutting edges thereby restricting everyday use of the vitreotome. In this connection, ultrasound instruments such as phacoemulsifiers or fragmentors find an increasingly wide application.
U.S. Pat. No. 3,693,613 describes an apparatus for the removal of material and a method of applying high frequency vibrations. The device comprises an ultrasonic generator, magnetostriction converter, a suction means for the removal of broken tissue, and a hollow needle having a through longitudinal bore. The needle is connected to the magnetostriction converter wherefrom it receives longitudinal periodic vibrations with a frequency of about 40 KHz and an amplitude of about 30 .mu.m. The free end portion of the needle when advanced contiguous to the lens breaks the nucleus to dust-like particles. Simultaneously, another route is used to introduce normal saline into the eyeball to dilute the broken mass and perform its aspiration via the through longitudinal bore of the needle using the suction unit provided with a pump and a motor.
A serious disadvantage of this device is the need of forcibly aspirating the broken mass by employing a special means provided with a pump. Continuous operation of the pump required throughout the extent of surgery poses the danger of abrupt pressure fluctuations within the suction system if the needle becomes blocked by large fragments broken off the lens. Such blockage of the suction channel produces surplus vacuum. Sudden dislodgement of obstruction due to changed power or frequency of the ultrasonic generator results in too much intraocular matter being sucked into the vacuum area since inertia of the feeding system delays restoration of the intraocular fluid balance. This may lead to such grave complication as ocular collapse.
The additional presence of an electric motor significantly complicates the device reducing its reliability due to a large number of moving parts and electric contact.
Moreover, the use of such a device is restricted to the removal of the lens mass, while the vitreous and other pathologically affected tissues remain inaccessible.
Another ultrasonic device designated medical machine for performing surgery and treating using the ultrasonic energy is disclosed in U.S. Pat. No. 3,990,452. The essential design of this device is similar to that mentioned above with all the inherent shortcomings thereof. However, from the above-described arrangement it is distinguished by a changed shape of the needle having a tapering neck such that its apex develops into an elongated cylindrical portion terminating by an obliquely cut end. A needle of this type allows fragmentation and aspiration of the lens mass, but its application can be extended to the vitreous and a variety of pathological tissues, for example, fibrin membranes, exudates, etc. However, such a needle is designed for a single surgery due to quick wear at the juncture of the conical and cylindrical portions.